The Conceptualization and Derivation of the Cervical Lordosis Distribution Index.

STUDY DESIGN/

SETTING

Retrospective cohort.

OBJECTIVE

Tailor correction of cervical deformity by incorporating the cervical apex into a distribution index [Cervical Lordosis Distribution Index (CLDI)] to maximize clinical outcomes while lowering rates of junctional failure.

BACKGROUND

Yilgor and colleagues developed the lumbar Lordosis Distribution Index to individualize the pelvic mismatch to each patient's pelvic incidence. The cervical lordosis distribution in relation to its apex has not been characterized.

PATIENTS AND

METHODS

Cervical deformity patients with complete 2Y data were included. The optimal outcome is defined by no distal junctional failure (DJF), and meeting "good clinical outcome (GCO)" criteria by Virk and colleagues: [meeting 2 of 3: (1) a Neck Disability Index <20 or meeting minimally clinically important difference, (2) modified Japanese Orthopedic Association ≥14, (3) an Numerical Rating Scale-neck ≤5 or improved by 2 or more points]. C2-T2 lordosis was divided into cranial (C2 to apex) and caudal (apex to T2) arches postoperatively. A CLDI was developed by dividing the cranial lordotic arch (C2 to apex) by the total segment (C2-T2) and multiplying by 100. Cross-tabulations developed categories for CLDI producing the highest χ 2 values for achieving optimal outcomes at 2 years and outcomes were assessed by multivariable analysis controlling for significant confounders.

RESULTS

Eighty-four cervical deformity patients were included. Cervical apex distribution postoperatively was: 1% C3, 42% C4, 30% C5, and 27% C6. The mean CLDI was 117 ± 138. Mean cranial lordosis was 23.2 ± 12.5°. Using cross-tabulations, a CLDI between 70 and 90 was defined as "'aligned." The χ 2 test revealed significant differences among CLDI categories for distal junctional kyphosis, DJF, GCO, and optimal outcome (all P < 0.05). Patients aligned in CLDI were less likely to develop distal junctional kyphosis [odds ratio (OR): 0.1, (0.01-0.88)], more likely to achieve GCO [OR: 3.9, (1.2-13.2)] and optimal outcome [OR: 7.9, (2.1-29.3)] at 2 years. Patients aligned in CLDI developed DJF at a rate of 0%.

CONCLUSION

The CLDI, classified through the cranial segment, takes each unique cervical apex into account and tailors correction to the patient to better achieve GCOs and minimize catastrophic complications after cervical deformity surgery.

LEVEL OF EVIDENCE: Level III.